Abstract
Nonmuscle myosin-2 (NM2) is a fundamental actin-based mechanochemical ATPase that regulates cellular architecture, migration, adhesion, and force generation across diverse biological contexts. NM2 function is tightly regulated by a structural transition between an autoinhibited monomeric (10S) conformation in which ATPase activity, actin binding, and filament assembly are coordinately suppressed and an enzymatically active, filamentous conformation. The autoinhibited conformation is critical for the spatial and temporal control of contractility in nonmuscle cells, yet structural insights into the 10S conformation remain largely elusive. Here, we present the cryo-EM structure of full-length human NM2B in the 10S conformation at ~5.24 Å resolution. The structure reveals a tri-segmented tail fold that introduces asymmetric interactions between both myosin heavy chains and associated light chains and the sequestration of key interfaces required for actin binding and filament assembly. These structural insights provide a mechanistic foundation for understanding how regulatory post-translational modifications and disease-associated mutations shift NM2 conformational equilibria and may enable the development of structure-based interventions for cytoskeletal diseases including hearing loss, neurodegeneration, and cancer.